There has been widely known in the prior art an automatic transmission which is equipped with a gear transmission mechanism and a plurality of frictional engagement elements to be selectively applied by the action of a hydraulic control unit so that any of a plurality of gear stages including a reverse stage may be established.
In this automatic transmission, a serious load torque is applied to the frictional engagement elements especially at the reverse time having a high gear ratio. Thus, there have been proposed a variety of counter-measures For the serious load torque.
Japanese Patent Laid-Open No. 129162/1991 has disclosed a system which is enabled to improve the durability of the frictional engagement elements and reduce the size of the frictional engagement elements by decreasing the engine torque when the reverse gear stage is established.
Moreover, Japanese Patent Laid-Open No. 166428/1992 has disclosed a system which is enabled to reduce the load torque when the reverse gear stage is established or maintained, by setting the auxiliary transmission portion to the high gear stage when the reverse stage is established.
incidentally, in case the engine torque-down to be effected when the reverse stage is established is executed by delaying the ignition time, for example, the timing for the delay is restricted of itself from the standpoint of preventing the overheat. This makes it impossible to continue the reduction of the load torque for a long time after the establishment of the reverse stage.
In case, moreover, the auxiliary transmission portion is set to the high gear stage, the number of the frictional engagement elements to be applied for the shift to the reverse stage is increased to drop the line pressure for the application thereby to elongate the time period till the application end (i.e., the establishment of the reverse stage) and to elongate the time period for the applications. As a result, the durability of the frictional engagement elements is not always improved.